This invention relates to optical instruments in which collimated rays of light must be positioned precisely.
In the manufacture of laser construction alignment instruments, for example, it is necessary that the beam correspond to a mechanical or optical reference. This is accomplished by either steering the beam or altering a mechanical reference. The reference could be an external housing, the axis of a level vial, or another beam of light. This invention has to do with steering or angularly adjusting the beam to correspond to a reference.
Beam adjusting or steering is typically done using an optical element such as a mirror, prisms, or a lens. FIG. 1 shows some typical methods of adjusting the beam angle by tilting a mirror with an adjustment screw. Fine motion of the beam is difficult in this method because there is a two-to-one relationship between the mirror angle and the beam angle. In addition, pitch of the screw must be fine to allow small angles of tilt.
An alternate method of finely steering a beam of light is shown in FIG. 2. Translating the lens in the direction of the arrow steers the beam in the upward direction. This method is attractive because the sensitivity can be controlled by the focal length of the lens.
FIG. 3 shows the use of rotatable prisms to steer a beam. When the prism is rotated about the axis of the incoming beam, the outgoing beam moves on an arc. By using two such prisms at 90 degrees to each other, each rotatable about the incoming beam, the outgoing beam may be finely adjusted in any desired direction.
The three methods shown in the figures require several mechanical parts to provide the adjustment and lock it in place as is required in any rugged instrument. These methods are, therefore, costly. Such instruments must also be hermetic which further adds to the cost because of the need for a sealed window.
The subject invention provides a method for finely steering, i.e., angularly adjusting, a collimated beam of light using a single low cost plastic optic, while hermetically sealing the instrument at the same time. The invention comprises a one piece very low magnification telescope design.
In a conventional telescope focused at infinity and viewed by a perfect observer's eye, a collimated beam of light enters the telescope, is magnified, and exits the telescope as a collimated beam of light. As shown in FIG. 4, in a like manner, rays at an angle A to axis C of the telescope are magnified by M, where M is the telescope's magnification. The angular deviation of the beam, however, is A.times.(M-1) as shown. For a telescope of magnification 1.01, this is a 1% angular deviation of the beam.
To observe the effect of tilting the telescope, we may tilt the entire system shown in FIG. 4 without changing the optical paths. As can be seen from FIG. 5, tilting the telescope by an angle A causes a beam deviation of M-1times A. In this way very fine control of the beam pointing can be obtained by tilting such a weak telescope.
Such a low magnification telescope can be easily fabricated as a single plastic or glass optic. FIG. 6 shows the construction details of the optic. In a typical design with a 1.012 magnification, the radii and thickness are 121.4 mm, 120 mm, and 2.92 mm, respectively, for an acrylic plastic optic. Such a telescope could be tilted +/-5 degrees to obtain +/-3.6 minutes of adjustment of the transmitted beam. For some alignment purposes, it is sometimes beneficial to have a net prism deviation or variable net optical wedge function in the optic to allow for fixed misalignment. This can be installed in the same optic with no loss of performance, and it combines the benefits of a thin optical wedge with the adjustment feature of the telescope itself, without requiring two separate optical elements. The optical wedge shifts the beam angle adjustment center, increasing adjustment in one direction; the optical element can be rotated to position the increased effect in the direction desired. The low magnification telescope, adjustable on assembly, is thus equivalent to a variable optical wedge.
When the optic is provided with an approximately spherical surface at the edges of the optic it can be easily tilted and provide a hermetic seal.
It is among the objects of the invention to provide a simple, inexpensive and reliable angular adjustment for a tool projecting a light beam for measurement, alignment or other purposes. This and other objects, advantages and features of the invention will be apparent from the following description of a preferred embodiment, considered along with the accompanying drawings.